Magnetrons



Dec. 13, 1955 F. c. THOMPSON ETAL 2,727,185

MAGNETRONS Filed Dec. 27, 1951 2 Sheets-SheeI l Dec- 13, 1955 F. c. THOMPSON ET A1. 2,727,185

MAGNETRONS F led Dec. 27. 1951 2 Sheetsfshee 2 z/r/f gai/244095:

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United States Patent C 2,727,135 MAGNETRONS.

Frederick CharlesM ThmPSQD, Danbury, Maurice.. Ester.-

son, Great Baddow, and A@richie WatsonI Crook, Chelmsford, England, assignorstoEnglish Electric Valve Com- Pany`Li1`11ite,'Llid0n, England, company 0f Great Britain.

Application December27, 1951, SerialNo. 263,642

Claims priority, application Great Britain,

* January 115.1951

6 Claims. (Cl. S15-39.71).

This invention relates to magnetrons and more specically to mangnetrons of the so-called packaged type i. e.` the type in which, in order to reduce` the,i length of the air gap inthe magnetic circuita the discharge envelope is'completed members of magnetic material which also form part of themagnetic circuit so that, in eect, the magnetic poles are brought inside the envelope.

Although packaged magnetrons have the advantage over the non-packaged types that, owing to the improved magnetic system, they can bey made. outA substantially reduced weight and size, this advantage is accompanied, in known packaged magnetrons, by appreciable loss of efficiency. This loss is due tothe fach that, inY known padtased magnetrgns, it` isV @practicable t provide the sofcalledv end` caps-4. e. discs otrnuch` greater diameter than that of the activatedl part of thecathode structurewhich, in the non-packaged types, prevent electrons leaving the cathodefanode space andbeingA collectedby-parts of the anode structure other than the anode segments. Current to parts of the anode structure other than the anode segments involves wasted power and is a cause of low conversion efficiency in packaged magnetrons. The present invention seeks to provide packaged magnetrons of improved eiliciency.

he nature of the difficulties which the present invention seeks to avoid Will be more fully explained in connection with the drawings accompanying the speciiication in which Fig. l shows, in section, the essential parts of a typical known magnetron of the non-packaged type; Fig. 2 is a similar view of a typical known packaged mangetron; and Fig. 3 is a similar View of an embodiment of this invention. Like references indicate like parts in all the gures.

lu Fig. l the cathode 1, heated by an internal heater 2 is axially situated within a copper anode structure 3 having anode segments 4. The structure 3 forms part of the discharge space envelope which is completed by at copper side plates 5 and located between the poles 6 of the magnet system. The magnetic gap is, as will be seen, a long one, being indicated by the dimension M. The cathode structure is supported by support members 7 which enter the envelope from the side and extend more or less at right angles to the axis. End caps in the form of discs 8 prevent electrons leaving the anode cathode space and being collected by parts of the anode structure other than the anode segments. The discs 8 thus serve to maintain a high conversion eiciency but their presence as well as that of the transverse support structure for the cathode, and that of the side plates 5, results in a long air gap M with consequent necessity to provide a heavy and bulky magnet system.

In the typical known packaged magnetron shown in Fig. 2 the air gap length M is much reduced, with consequent ability to use a much stronger magnetic eld with the same or a smaller magnet system, by dispensing with the side plates 5, using the pole pieces 6 as part of the envelope structure, and supporting the cathode structure by means, generally designated 7a, which run f'ce axially through a hole in one of the pole pieces instead this requirement strictly' limits the maximum diameterA which can be tolerated for the hole in the pole piece. lf the hole is made appreciably greater in diameter than that of the cathode theviield configuration at the cathode surface is poor. ltV is therefore impracticable to tit large end caps such as the caps 8A of Fig. 1,l for a cathode structure with such caps would not pass, in assembly, through the necessarily small hole in the pole piece and', in general, it is, ify not absolutely-impossible, at any rate very diiicult and impracticable for lmanufacturing rea,- sons to fit the endy caps to the cathode structure after the latter hasbeen mounted on the pole, piece.V It'has therefore been the practice, with known packagedniagnen trous, either to omit end caps altogether or to be content with very small endcaps with resultant waste power and loss of eiliciency. Incidentally the waste power,l in any-.given case depends critically on the geometryiofthe mangetron notably on the eccentricity of' the cathode with respect to the anode andthe space between any small end captted on the pole piece and. can increase during the operating life ota magnetron, The absence oi end caps, or the use of caps of, insuicient size can therefore reduce the usefullife of a magnetron byA bringing forward the time when its outputV power is Vinsuflcient forv it to be stillregarded as usefuh According to this invention in itsvbroadest aspectpat leastk part` of the pole piece ofa packaged magnetronuis insulated fromV the anode structure so that it may be maintained at cathode or other desired potential and thereby serve as an end cap to prevent electrons straying from the anode-cathode space.

ireferably the pole piece consists of two concentric parts insulated from one another of which the outer part is attached as in a known packaged magnetron, to the anode structure and therefore takes the potential thereof and the inner part, which acts also as an end cap, is connected to the cathode.

In Fig. 2 the pole pieces are shown of composite construction instead of single pole piece arrangement because, if the ends of the pole pieces 6 in Fig. 2 were made wider they would merely increase the emission from the ends of the cathode. Such a construction would in fact tend to detract from the action of the magnetron and it was for the purpose of avoiding such difliculty that the pole piece was made into two concentric parts, of which the inner part is held at the cathode potential.

Fig. 3 shows an embodiment of the invention. In this drawing the cathode 1 is heated by an internal heater 2 and is located axially within a multiplecavity anode F structure 3 having anode segments 4. The cathode structure is supported by means indicated at 7a which run axially through a hole within the inner part 6b of the pole piece. Each pole piece is divided into two concentric parts 6a, 6b which are insulated from one another, the outer part 6a being connected to the anode structure as in Fig. 2 and the inner part 6b providing the required end cap action. As will be seen the effective end cap-the tip 9 of the inner part (Jb-may be made as large as desired while still retaining only a small hole through it for the cathode support structure. Both poles are similarly formed. That which accommodates the cathode supports, that is the upper part in Fig. 3, has its inner part 6b connected to the cathode. The corresponding part 6b of the other pole may also be connected to the cathode, either externally or internally, or it may be left floating. Fig. 3 also shows how the top ends of the inner and outer parts 6a and 6b are maintained in insu- 3 lated relation to each other. The pole pieces 6a and 6b connect with the anode structure 3 through cylindrical elements 10 brazed to the pole pieces by brazing material represented at 11.

We claim:

l. A magnetron structure comprising an axial cathode structure, a multiple anode structure concentrically surrounding said cathode structure and providing an electron discharge space between said anode and cathode structures, magnetic pole pieces forming part of a magnetic circuit adapted to provide lines of force threading said discharge space in a direction substantially parallcl to said cathode structure, an evacuated envelope of which part is constituted by said anode structure and part by said pole pieces, and an end cap positioned adjacent an end of said discharge space and adapted to prevent electrons straying from the said discharge space, said end cap being constituted by a portion of said pole piece insulated from said anode structure and concentn'cally within another portion of said pole piece which surrounds said irst mentioned portion, and is insulated therefrom.

2. A magnetron structure comprising an axial cathode structure, a multiple anode structure concentrically surrounding said cathode structure and providing an electron discharge space between said anode and cathode structures, a pair of magnetic pole pieces, one adjacent each end of said discharge space and forming parts of a magnetic circuit adapted to provide lines of force threading said discharge space in a direction substantially parallel to said cathode structure, an evacuated envelope of which part is constituted by said anode structure and parts by said pole pieces, and a pair of end caps positioned adjacent the ends of said discharge space and adapted to prevent electrons straying from said discharge space, said end caps being constituted each by a portion of a pole piece, each of said pole pieces consisting of an outer portionand an inner portion which is insulated from said outer portion, the ends of said inner portion constituting said end caps and one of said inner portions having a central hole adapted to pass the cathode structure in manufacture.

3. A magnetron as claimed in claim 2 in which said pole piece consists of two concentric parts insulated from one another of which the outer part is attached to the anode structure of the magnetron and the inner part is adapted to receive a desired operating potential.

4. A magnetron according to claim l wherein said pole piece consists of two concentric parts insulated from one another of which the outer part is attached to the anode structure of'the magnetron and the inner part is adapted to receive a desired operating potential.

5. A magnetron according to claim 2 and having a pole piece consisting of two concentric parts insulated from one another of which the outer part is attached to the anode structure of the magnetron and the inner part is connected to the cathode of the magnetron.

6. A magnetron according to claim 1 and having a pole piece consisting of two concentric parts insulated from one another of which the outer part is attached to the anode structure of the magnetron and the inner part is connected to the cathode of the magnetron.

References Cited in the iile of this patent UNITED STATES PATENTS 2,305,884 Litton Dec. 22, 1942 2,419,172 Smith Apr. 15, 1947 2,497,436 Brown Feb. 14, 1950 FOREIGN PATENTS 509,102 Great Britain July 11, 1939 

